Improving Debugging And Testing Through Assertions

Reading through the The Typemock Insider blog, I came across this post from Gil Zilberfeld.

I myself tend to fall in Gil’s practice ("binary search" debugging), but I don’t think Kent Beck has the right solution.

Gil’s suggestion of using Isolator is tempting (I don’t miss an opportunity to use it), but still not my favorite one.

I prefer to use debug assertions. Debug assertions can be used when running a debug version of the application to pop-up assertion messages and when running unit tests to fail tests.

In order to use debug assertions in unit tests a “special” trace listener is needed to make the test fail when its Fail method is called.

public class UnitTestTraceListener : global::System.Diagnostics.DefaultTraceListener
{
public UnitTestTraceListener() : base()
{
this.Name = "UnitTest";
this.AssertUiEnabled = false;
}

<span style="color: blue">public override void </span>Fail(<span style="color: blue">string </span>message, <span style="color: blue">string </span>detailMessage)
{
    Microsoft.VisualStudio.TestTools.UnitTesting.<span style="color: #2b91af">Assert</span>.Fail(<span style="color: #a31515">&quot;Debug.Assert Failed: &quot; </span>+ message + <span style="color: #a31515">&quot; &quot; </span>+ detailMessage);
}

}

Now, all you need to do is register it.

Registering the trace listener can either be done in code:

System.Diagnostics.Trace.Listeners.Remove("Default");
System.Diagnostics.Trace.Listeners.Add(new UnitTestTraceListener());

or configuration:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.diagnostics>
    <assert assertuienabled="false"/>
    <trace>
      <listeners>
        <clear/>
        <add name="UnitTest" type="UnitTestTraceListener"/>
      </listeners>
    </trace>
  </system.diagnostics>
</configuration>

And if I’m using Isolator I have the take in account the accesses made in the call to the Assert method. More fun to me.